As depicted in FIGS. 9A, 9B, joints between two workpieces, e.g. two pieces 211, 213 of wood when making furniture, can be made by gluing a thin, wooden wafer 215 ("biscuit" or "spline") in the two workpieces 211, 213. To do this, a similar size slot 217, 219 is made in each workpiece 211, 213 and glue is applied in the slots 217, 219 and/or on wafer 215. The wafer 215 is inserted in one slot to approximately one-half the width of the wafer. Then the two workpieces 211, 213 are then clamped together until the glue sets. If desirable, several such wafers 215 can be inserted into a mating slot 217, 219 in each workpiece 211, 213 at spaced locations throughout the joint. All such wafers are partly assembled in one of the workpieces before the two workpieces 211, 213 are clamped together.
Portable power tools, commonly known as biscuit or plate joiners, have been developed for making the wafer receiving slots by plunge cutting. As shown in U.S. Pat. No. 4,913,204, the plunge cut can be made by reciprocally moving along a linear path a motor housing relative to a shoe assembly of the joiner to cause a circular blade to protrude forwardly through and to retract rearwardly through an opening in the shoe assembly. In another known type, the plunge cut is made by reciprocally pivoting a motor housing relative to a shoe assembly of the joiner to cause a circular blade to protrude forwardly through and to retract rearwardly through an opening in the shoe assembly. In another known type of joiner described in U.S. Pat. No. 4,947,908, a motor housing is pivotally mounted relative to a shoe assembly and the cut is made by sweeping, rather than plunging, an elongated, generally cylindrical bit through an opening in the shoe assembly.
In all of the foregoing joiner types, when making the cut, lateral forces are imposed on the workpiece by the blade or cutter tending to cause the workpiece to slide relative to the shoe assembly. In the circular blade joiners, the rotation of the blade generates the lateral forces. In the cylindrical bit joiners, the sweeping action of the bit into the workpiece causes the lateral forces. Thus for accuracy, these lateral forces must be overcome to retain the shoe assembly in a fixed location on the workpiece when the cut is made. In prior art joiners, a number of different mechanisms have been used to increase the lateral stability of the joiner shoe relative to the workpiece. One mechanism is a retractable spring biased metal pin which is embedded in the workpiece when the shoe is engaged with the workpiece to make a cut. Other known mechanisms have a rubber coated or sand paper coated shoe surface for engaging the workpiece. See, for example, U.S. Pat. No. 4,947,908 (FIG. 10). In another mechanism, rubber plugs are inset in and project from a shoe surface for engaging the workpiece.
These prior art mechanisms suffer from certain disadvantages. The spring biased metal pin while increasing the lateral stability of the joiner is not preferred by some users because the pin can permanently damage the workpiece if inadvertently engaged with an exposed surface of the workpiece. Also, the pin restricts the sliding of the joiner relative to the workpiece when positioning the joiner relative to the workpiece at the desired location for making a cut. The rubber coated or sand paper coated mechanisms and the rubber plugs are disadvantageous because they provide less lateral stability of the joiner on the workpiece. And, therefore, these mechanisms have a greater tendency to permit relative sliding between the joiner and the workpiece when making a cut. This is particularly true if the shoe and workpiece surfaces are dusty.